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Chapter 7. Expanding persistent volumes
7.1. Enabling volume expansion support
Before you can expand persistent volumes, the StorageClass
object must have the allowVolumeExpansion
field set to true
.
Procedure
Edit the
StorageClass
object and add theallowVolumeExpansion
attribute by running the following command:$ oc edit storageclass <storage_class_name> 1
- 1
- Specifies the name of the storage class.
The following example demonstrates adding this line at the bottom of the storage class configuration.
apiVersion: storage.k8s.io/v1 kind: StorageClass ... parameters: type: gp2 reclaimPolicy: Delete allowVolumeExpansion: true 1
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- Setting this attribute to
true
allows PVCs to be expanded after creation.
7.2. Expanding CSI volumes
You can use the Container Storage Interface (CSI) to expand storage volumes after they have already been created.
CSI volume expansion does not support the following:
- Recovering from failure when expanding volumes
- Shrinking
Prerequisites
- The underlying CSI driver supports resize.
- Dynamic provisioning is used.
-
The controlling
StorageClass
object hasallowVolumeExpansion
set totrue
. For more information, see "Enabling volume expansion support."
Procedure
-
For the persistent volume claim (PVC), set
.spec.resources.requests.storage
to the desired new size. -
Watch the
status.conditions
field of the PVC to see if the resize has completed. OpenShift Container Platform adds theResizing
condition to the PVC during expansion, which is removed after expansion completes.
7.3. Expanding FlexVolume with a supported driver
When using FlexVolume to connect to your back-end storage system, you can expand persistent storage volumes after they have already been created. This is done by manually updating the persistent volume claim (PVC) in OpenShift Container Platform.
FlexVolume allows expansion if the driver is set with RequiresFSResize
to true
. The FlexVolume can be expanded on pod restart.
Similar to other volume types, FlexVolume volumes can also be expanded when in use by a pod.
Prerequisites
- The underlying volume driver supports resize.
-
The driver is set with the
RequiresFSResize
capability totrue
. - Dynamic provisioning is used.
-
The controlling
StorageClass
object hasallowVolumeExpansion
set totrue
.
Procedure
To use resizing in the FlexVolume plugin, you must implement the
ExpandableVolumePlugin
interface using these methods:RequiresFSResize
-
If
true
, updates the capacity directly. Iffalse
, calls theExpandFS
method to finish the filesystem resize. ExpandFS
-
If
true
, callsExpandFS
to resize filesystem after physical volume expansion is done. The volume driver can also perform physical volume resize together with filesystem resize.
Because OpenShift Container Platform does not support installation of FlexVolume plugins on control plane nodes, it does not support control-plane expansion of FlexVolume.
7.4. Expanding local volumes
You can manually expand persistent volumes (PVs) and persistent volume claims (PVCs) created by using the local storage operator (LSO).
Procedure
- Expand the underlying devices. Ensure that appropriate capacity is available on these devices.
-
Update the corresponding PV objects to match the new device sizes by editing the
.spec.capacity
field of the PV. -
For the storage class that is used for binding the PVC to PVet, set
allowVolumeExpansion:true
. -
For the PVC, set
.spec.resources.requests.storage
to match the new size.
Kubelet should automatically expand the underlying file system on the volume, if necessary, and update the status field of the PVC to reflect the new size.
7.5. Expanding persistent volume claims (PVCs) with a file system
Expanding PVCs based on volume types that need file system resizing, such as GCE, EBS, and Cinder, is a two-step process. First, expand the volume objects in the cloud provider. Second, expand the file system on the node.
Expanding the file system on the node only happens when a new pod is started with the volume.
Prerequisites
-
The controlling
StorageClass
object must haveallowVolumeExpansion
set totrue
.
Procedure
Edit the PVC and request a new size by editing
spec.resources.requests
. For example, the following expands theebs
PVC to 8 Gi:kind: PersistentVolumeClaim apiVersion: v1 metadata: name: ebs spec: storageClass: "storageClassWithFlagSet" accessModes: - ReadWriteOnce resources: requests: storage: 8Gi 1
- 1
- Updating
spec.resources.requests
to a larger amount expands the PVC.
After the cloud provider object has finished resizing, the PVC is set to
FileSystemResizePending
. Check the condition by entering the following command:$ oc describe pvc <pvc_name>
-
When the cloud provider object has finished resizing, the
PersistentVolume
object reflects the newly requested size inPersistentVolume.Spec.Capacity
. At this point, you can create or recreate a new pod from the PVC to finish the file system resizing. Once the pod is running, the newly requested size is available and theFileSystemResizePending
condition is removed from the PVC.
7.6. Recovering from failure when expanding volumes
If expanding underlying storage fails, the OpenShift Container Platform administrator can manually recover the persistent volume claim (PVC) state and cancel the resize requests. Otherwise, the resize requests are continuously retried by the controller.
Procedure
-
Mark the persistent volume (PV) that is bound to the PVC with the
Retain
reclaim policy. This can be done by editing the PV and changingpersistentVolumeReclaimPolicy
toRetain
. - Delete the PVC.
-
Manually edit the PV and delete the
claimRef
entry from the PV specs to ensure that the newly created PVC can bind to the PV markedRetain
. This marks the PV asAvailable
. - Re-create the PVC in a smaller size, or a size that can be allocated by the underlying storage provider.
-
Set the
volumeName
field of the PVC to the name of the PV. This binds the PVC to the provisioned PV only. - Restore the reclaim policy on the PV.
Additional resources
-
The controlling
StorageClass
object hasallowVolumeExpansion
set totrue
(see Enabling volume expansion support).